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You noticed that your senior cat’s fur has been looking pretty scruffy lately. He’s been eating like crazy, but he’s still losing weight. He’s suddenly acting hyper and crying in the night, and when you go to clean the litter box, it’s flooded with pee. You know something’s wrong, that it’s a health issue, so you take Fluffy to the vet. A blood test reveals that he has feline hyperthyroidism. So, what do you do about hyperthyroidism in cats?

First, you have to understand what you’re dealing with. Here are some questions and answers to get you started.

1. What are the thyroid glands?

The thyroid glands are two tiny bits located on either side of your cat’s trachea (windpipe). Their job is to produce hormones that affect many of the body’s functions, but governing the rate at which your cat’s body burns energy is the most important when we’re discussing hyperthyroidism.

2. What goes wrong in feline hyperthyroidism?

A tumor grows on the thyroid glands and causes the body to produce too much thyroid hormone, which makes your cat’s body burn energy too quickly.

3. What are the symptoms of hyperthyroidism in cats?

Because your cat’s body is burning energy too quickly, the first thing you’ll probably notice is that your cat is always hungry and is losing weight in spite of his massive food consumption. He’ll also be drinking and urinating too much. Hyperthyroidism can produce behavior changes such as increased activity and restlessness, and sometimes even aggressiveness. Your cat’s fur will start looking greasy and unkempt.

4. How is hyperthyroidism in cats diagnosed?

Your vet will perform a blood test that measures the levels of thyroid hormones in your cat’s blood. If the levels of those hormones are high, your cat is hyperthyroid.

5. What treatments are available for feline hyperthyroidism?

There are three common forms of treatment for hyperthyroidism in cats: medication, radioactive iodine therapy and surgery. All three have risks and benefits.

Medication — typically methimazole (Tapazole) here in the United States — decreases the level of thyroid hormone in your cat’s blood. It is available as a pill or in the form of a gel, which is applied to your cat’s skin. Most cats tolerate methimazole pretty well. Medication seems like the least expensive option, but in the long run the costs can add up.

Radioactive iodine (I-131) therapy is considered the gold standard of treatment, but you may have trouble finding a clinic that offers it within a reasonable distance. It is pretty expensive, but the good news is that once the treatment is done, your cat’s hyperthyroidism is cured.

Surgery to remove the thyroid gland is an option, but it may not solve the problem. There may be tumor cells in other parts of your cat’s body that continue to overproduce thyroid hormone, or removal of the gland could mean he’ll no longer produce enough thyroid hormone and will have to be on medicine for the rest of his life.

6. What about prescription food for hyperthyroid cats?

This food is designed to be too low in iodine, a chemical that helps the thyroid glands produce hormones. It’s being heavily marketed to vets and cat lovers, but among the vets I know, there’s a good deal of controversy about whether it has been adequately studied and what effects the lack of iodine might have on a cat’s overall health.

7. What are the complications of hyperthyroidism in cats?

Feline hyperthyroidism can disguise other conditions like kidney disease, because “running too hot” improves kidney function. Some other possible complications include high blood pressure, heart problems and difficulty breathing.

Hyperthyroidism in cats is a disease that can be managed, but it requires commitment on your part and good communication between you and your veterinarian.

Do you have a cat with hyperthyroidism? Which treatments have you tried, and how did they work out for you? Are there support groups you’d recommend? Please share your experiences in the comments.

About JaneA Kelley: Punk-rock cat mom, science nerd, animal shelter volunteer, and all-around geek with a passion for bad puns, intelligent conversation, and role-play adventure games. She gratefully and gracefully accepts her status as chief cat slave for her family of feline bloggers, who have been writing their cat advice column, Paws and Effect, since 2003. JaneA dreams of making a great living out of her love for cats.

14 comments on “7 Things You Need to Know About Hyperthyroidism in Cats”

My Dixie was diagnosed April of last year. There is no way I can get a pill in her so the prescription diet is the option I chose as the cream for some reason isn’t available to me. It is working and I’ve got my healthy girl back! However, I am braced for the day the diet actually causes other problems, as there are so many crap ingriedients in it. Only one company is manufacturing it and there are no treats available either.
In the meantime, I am happy to just have a happy healthy kitty again!

Our cat “Midnight” was a feral cat that turned into a loving house cat. He was diagnosed with hyperthyroidism in February 17. We opted for the removal of one thyroid that was damaged, the other was healthy. No further meds were ordered after the procedure in March. He died one month later. We estimated his age to be 12 when he died. He was with us for almost 7 years. He was a great cat!

We use transdermal methimazole in alternating ears. We do a dose in the morning and evening every day. Works like a charm and our girl takes it like a champ. WAY better than trying to force a pill down her throat.. which would be nearly impossible with this cat. Feisty is an understatement. We also use CBD in the evenings to help her anxiety that has come with the disease. She’s fat and happy again… and so are we!

My 15 yr old Cornish Rex has hyperthyroidism. He’s also had HCM since he was six, so fortunately he’s used to taking medication. He vomited with the pill so we’re using the transdermal ointment and he’s doing well for his age and condition. I just alternate ears and make sure to clean them every couple of days to prevent build-up. I also get medical gloves and cut off the fingers to use as finger cots when applying the medication.

My 15 yr old male cat had this. I had experience pilling another cat and didn’t want to alienate this one. I paid $1200 for the radiation treatment in 2007 and he was completely cured and lived for another 4 years. For me it was 100% worth it! If you can afford it I would highly recommend it!

Our 12 year old Princess has been recently diagnosed with Hyperthyroid. She now runs away from me every time I approach her as she thinks I’m gonna force a pill down her throat..that I do twice daily. Ugh.

My cat was recently diagnosed as well. We use a flavored (tuna) compounded pill that we get from the vet. It is probably a little more expensive (about $30/month) than the regular pills but is so easy! My cat thinks it is a treat and begs for it every time we go to the kitchen. Good luck with your kitty!

Thanks so much for your article. My Ragdoll cat – Lola is quite old – over 18 years I think.
I am not sure as I am the third owner. I have her for well over 10 years. She developed
the problem about a year ago. Eating and losing weight, drinking all the time and crying all the time. With in 3 days on medication she was her old self – I could not believe it. She is back to her old ways – quite affectionate and purring when happy – what a change. And – she does not look her age.

I am a bit confused. In humans, the cause of hyperthyroidism is NOT from a tumor. It is, I think, one of those idiopathic diseases where there is no known cause. Why would this be different in felines? I once had a cat who had this. Yes, she lost weight and ate and drank a lot. She was put on medication, and the problem got better. NO tumor was found. Please explain a bit more.